projects/08/src/codewriter.h
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#ifndef _CODEWRITER_H
#define _CODEWRITER_H
// 'codewriter.h' roughly corresponds to the 'CodeWriter' module specified in
// nand2tetris, with a few liberties taken.
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "parser.h"
#include "util.h"
#define _DEBUG
// memory mapping:
// 0-15 virtual registers R0-R15
// 16-255 static variables
// 256-2047 stack
#define SP (0) // points to word ahead of top of stack
#define LCL (1) // points to local segment
#define ARG (2) // points to argument segment
#define POINTER (3)
#define THIS (3)
#define THAT (4)
#define TEMP (5)
#define R13 (13) // R13-R15 are scratch space that
#define R14 (14) // VM-generated assembly can use
#define R15 (15) // for whatever.
#define STATIC (16) // start of static variables segment (240 words, 16-255)
char *static_sym_name;
// retrieve hack assembly RAM offset given static "symbol" number
#define MAX_STATIC_SYMBOLS (240) // for whatever.
uint16_t static_symbol_map[MAX_STATIC_SYMBOLS]; // 0..239 maps to 16..255
uint8_t g_symbol_offset_start = 0; // set to g_symbol_offset_stop on new file
uint8_t g_symbol_offset_stop = 0; // bump when new static number (sym) found
char comp_vm_funcs[] = "@__comp_funcs_end\n"
"0;JMP\n"
"\n"
"(__test_eq)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if D == 0, equal
"M=0\n" // prematurely push false
"@__test_eq_neq\n" // if D == 0, equal
"D;JNE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_eq_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__test_gt)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if (D - M) > 0; push true
"M=0\n" // prematurely push false
"@__test_gt_neq\n" // if D == 0, equal
"D;JLE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_gt_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__test_lt)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if (D - M) < 0; push true
"M=0\n" // prematurely push false
"@__test_lt_neq\n" // if D == 0, equal
"D;JGE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_lt_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__comp_funcs_end)\n";
char vm_init[] = "@261\n" // start address of stack (nothing pushed yet)
"D=A\n" // D = 261 (why? because we are simulating a
// "call", and a call would add 5 to SP, which
// is expected to be initialized to 256.
// TODO: verify if I also need to init LCL, ARG
// THIS/THAT etc... (I probably don't)
"@SP\n" // A = <constant representing address of SP>
"M=D\n" // <memory pointed to by SP> = 256
"@Sys.init\n" // jump to Sys.init function (not call since
"0;JMP\n\n"; // we don't need to set up the stack)
// TODO: add initializers for argument, local, static, this, that
// TODO only output vm_stop when Main.main
char vm_stop[] = "(END)\n" // starting address of stack (nothing pushed yet)
"@END\n" // D = 256
"0;JMP\n"; // A = <constant representing address of SP>
void write_vm_init(FILE *fp)
{
fprintf(fp, "%s", vm_init); // can (un)comment to toggle init behavior
fprintf(fp, "%s\n", comp_vm_funcs);
}
void write_vm_stop(FILE *fp)
{
fprintf(fp, "\n%s", vm_stop);
}
static bool write_arithmetic(struct vm_instruction_t *vm_instr, FILE *fp)
{
char binary_op_template[] = "@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"%s"; // arithmetic op goes here
char unary_op_template[] = "@SP\n"
"A=M-1\n" // A = SP - 1
"%s"; // arithmetic op goes here
char op_add[] = "M=D+M\n";
char op_sub[] = "M=M-D\n";
char op_eq[] = "@%s_%lu_eq\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_eq\n"
"0;JMP\n"
"(%s_%lu_eq)\n" // return here
"\n";
char op_gt[] = "@%s_%lu_gt\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_gt\n"
"0;JMP\n"
"(%s_%lu_gt)\n" // return here
"\n";
char op_lt[] = "@%s_%lu_lt\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_lt\n"
"0;JMP\n"
"(%s_%lu_lt)\n" // return here
"\n";
char op_and[] = "M=D&M\n";
char op_or[] = "M=D|M\n";
char op_neg[] = "M=-M\n";
char op_not[] = "M=!M\n";
// binary operations
if (!strncmp(vm_instr->arg1, "add", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_add);
} else if (!strncmp(vm_instr->arg1, "sub", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_sub);
} else if (!strncmp(vm_instr->arg1, "eq", CMD_STR_MAX_LEN)) {
fprintf(fp, op_eq, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "gt", CMD_STR_MAX_LEN)) {
fprintf(fp, op_gt, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "lt", CMD_STR_MAX_LEN)) {
fprintf(fp, op_lt, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "and", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_and);
} else if (!strncmp(vm_instr->arg1, "or", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_or);
// unary operations
} else if (!strncmp(vm_instr->arg1, "neg", CMD_STR_MAX_LEN)) {
fprintf(fp, unary_op_template, op_neg);
} else if (!strncmp(vm_instr->arg1, "not", CMD_STR_MAX_LEN)) {
fprintf(fp, unary_op_template, op_not);
} else {
err("error: invalid arithmetic op \"%s\"\n", vm_instr->arg1);
return false;
}
return true;
}
// attempt to either 1) resolve an existing static variable, or 2) associate
// the static variable with a new slot in the static section (which can later
// be resolved)
static bool resolve_static_address(struct vm_instruction_t *vm_instr,
uint16_t *addr)
{
uint16_t sym_offset;
// Basically, g_symbol_offset_start "indexes" into the VM files', and
// g_symbol_offset_stop indexes the last added static var per file.
// These variables serve as a window into static_symbol_map
if (g_symbol_offset_stop >= MAX_STATIC_SYMBOLS) {
err("error: symbol offset grew too large (>= %u), too many "
"static variables\n", MAX_STATIC_SYMBOLS);
return false;
}
for (sym_offset = g_symbol_offset_start;
sym_offset <= g_symbol_offset_stop; ++sym_offset) {
// found static "symbol" (number after push/pop static ...)
if (static_symbol_map[sym_offset] == vm_instr->arg2) {
*addr = sym_offset + 16;
return true;
}
}
// insert vm_instr->arg2 into next static_symbol_map slot
static_symbol_map[g_symbol_offset_stop] = vm_instr->arg2;
++g_symbol_offset_stop; // bump stop offset
*addr = (g_symbol_offset_stop - 1) + 16; // add 16 to map to RAM
return true;
}
// push 16-bit value from segment offset onto top of stack
static bool write_push(struct vm_instruction_t *vm_instr, FILE *fp)
{
uint16_t addr, arg2 = vm_instr->arg2;
// TODO: could add SP counter/check to catch overflows
char const_template[] = "@%hu\n" // A = constant
"D=A\n%s"; // D = constant
char addr_template[] = "@%hu\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char static_template[] = "@%s.%hu\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char indirect_template[] = "@%hu\n" // A = segment
"D=M\n" // D = RAM[segment]
"@%hu\n" // A = index
"A=A+D\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char push_boilerplate[] = "@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n"; // RAM[SP] = constant
if (!strcmp(vm_instr->arg1, "constant")) {
// TODO: check size of constant (allowed to be > 32,767?)
// TODO: look in nand2tetris forums in case issue already noted
fprintf(fp, const_template, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, indirect_template, ARG, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, indirect_template, LCL, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, static_template, static_sym_name, addr,
push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, indirect_template, THIS, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, indirect_template, THAT, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, addr_template, addr, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, addr_template, addr, push_boilerplate);
} else {
err("error: invalid segment name \"%s\"\n",
vm_instr->arg1);
return false;
}
return true;
}
// pop 16-bit value from top of stack into segment offset
static bool write_pop(struct vm_instruction_t *vm_instr, FILE *fp)
{
// TODO: could add SP counter/check to catch overflows
uint16_t addr, arg2 = vm_instr->arg2;
char pop_indirect_template[] = "@%hu\n" // @segment
"D=M\n" // D = segment
"@%hu\n" // @index
"D=A+D\n" // A = segment + index
"@R13\n"
"M=D\n" // RAM[13] = segment + index
"@SP\n" //
"AM=M-1\n" //
"D=M\n" //
"@R13\n" //
"A=M\n" //
"M=D\n"; //
char pop_addr_template[] = "@SP\n"
"AM=M-1\n" // decrement SP
"D=M\n" // "pop" (read) value into D
"@%hu\n" // load address
"M=D\n"; // "pop" (write) value to RAM
char pop_static_template[] = "@SP\n"
"AM=M-1\n" // decrement SP
"D=M\n" // "pop" (read) value into D
"@%s.%hu\n" // A = segment + index
"M=D\n"; // RAM[segment + index] = D
if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, pop_indirect_template, ARG, arg2);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, pop_indirect_template, LCL, arg2);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, pop_static_template, static_sym_name, addr);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, pop_indirect_template, THIS, arg2);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, pop_indirect_template, THAT, arg2);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, pop_addr_template, addr);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, pop_addr_template, addr);
} else {
err("error: invalid segment name \"%s\"\n",
vm_instr->arg1);
return false;
}
return true;
}
static bool write_label(struct vm_instruction_t *vm_instr, FILE *fp)
{
char label_asm[] = "(%s)\n";
fprintf(fp, label_asm, vm_instr->arg1);
return true;
}
static bool write_goto(struct vm_instruction_t *vm_instr, FILE *fp)
{
char goto_asm[] = "@%s\n"
"0;JMP\n";
fprintf(fp, goto_asm, vm_instr->arg1);
return true;
}
static bool write_if(struct vm_instruction_t *vm_instr, FILE *fp)
{
char if_asm[] = "@SP\n" // pop register D
"AM=M-1\n"
"D=M\n" // pop value into D register
"@%s\n"
"D;JNE\n";
fprintf(fp, if_asm, vm_instr->arg1);
return true;
}
//////////
//
// The Elements of Computing Systems, 2nd edition, pg. 214
//
// CALLING CONVENTIONS STACK DIAGRAM
// ===================================
// Low memory addresses
//
// ... similar blocks above ...
// |--------------------| \
// | some value | | Local variables/working stack of _caller_
// |--------------------| |
// | some value | |
// |--------------------| < -------- BEGIN FUNCTION CALL --------
// ARG -> | argument 0 | | Argument segment of _callee_:
// |--------------------| | Pushed by caller before calling
// | argument 1 | | callee using 'call' command.
// |--------------------| |
// | ... | |
// |--------------------| <
// LCL-5 -> | return address | | Saved frame of _caller_:
// |--------------------| | Pushed by the VM when handling
// LCL-4 -> | saved LCL | | the 'call' command.
// |--------------------| | When handling 'return', the VM
// LCL-3 -> | saved ARG | | pops these values and uses them
// |--------------------| | for restoring the memory segments
// LCL-2 -> | saved THIS | | of, and returning to, the caller's
// |--------------------| | code.
// LCL-1 -> | saved THAT | |
// |--------------------| <
// LCL -> | local 0 | | The local segment of _callee_:
// |--------------------| | Initialized by the VM when handling
// | local 1 | | the 'function' command.
// |--------------------| |
// | working stack... | | Working stack of _callee_
// |--------------------| <
// SP -> | < undefined > | |
// +--------------------+ |
// _||_ |
// direction stack \ / /
// grows (up) \/
//
// High memory addresses
//
static bool write_function(struct vm_instruction_t *vm_instr, FILE *fp)
{
size_t i, num_locals;
num_locals = vm_instr->arg2;
char set_local_boilerplate[] = "M=0\n"
"A=A+1\n";
char set_sp[] = "D=A\n" // D = number of locals
"@SP\n" // get address of SP
"M=D\n"; // set SP to new value
// (functionName) // injects function entry label into the code
// repeat nVars times: // nVars = number of local variables
// push 0 // initializes local variable to 0
fprintf(fp, "(%s)\n", vm_instr->arg1); // write function label
fprintf(fp, "@SP\n"); // get SP
for (i = 0; i < num_locals; ++i) {
fprintf(fp, "%s", set_local_boilerplate); // write 'push 0'
}
fprintf(fp, "%s", set_sp);
return true;
}
static bool write_return(FILE *fp)
{
/*
* frame = LCL // frame is a temporary variable
* retAddr = *(frame - 5) // put return address in a temporary variable
* *ARG = pop() // repositions the return value for the caller
* SP = ARG+1 // repositions SP for the caller
* THAT = *(frame - 1) // restores THAT for the caller
* THIS = *(frame - 2) // restores THIS for the caller
* ARG = *(frame - 3) // restores ARG for the caller
* LCL = *(frame - 4) // restores LCL for the caller
* goto retAddr // jump to where return address points
*/
char ret_boilerplate[] = "// *ARG = pop()\n"
"@SP\n"
"AM=M-1\n" // decrement A and SP
"D=M\n" // "pop" (read) return value into D
"@ARG\n"
"A=M\n" // A points to argument segment
"M=D\n" // *ARG = D // (D = pop())
"// SP = ARG+1\n"
"D=A+1\n" // A still contains arg pointer
"@SP\n"
"M=D\n"
"// frame = LCL\n"
"// THAT = *(frame - 1)\n"
"@LCL\n"
"AM=M-1\n" // decrement A and LCL
"D=M\n" // D = *(frame - 1)
"@THAT\n"
"M=D\n" // THAT = D
"// THIS = *(frame - 2)\n"
"@LCL\n"
"AM=M-1\n" // decrement A and LCL
"D=M\n" // D = *(frame - 2)
"@THIS\n"
"M=D\n"
"// ARG = *(frame - 3)\n"
"@LCL\n"
"AM=M-1\n" // decrement A and LCL
"D=M\n" // D = *(frame - 3)
"@ARG\n"
"M=D\n"
"// R13 = retAddr = *(frame - 5)\n"
"@LCL\n"
"AM=M-1\n" // decrement A and LCL
// now LCL = LCL - 4
"D=M-1\n" // D = *(frame - 4 - 1)
"@R13\n"
"M=D\n" // R13 = D (retAddr)
"// LCL = *(frame - 4)\n"
"@LCL\n"
"A=M\n" // put pointer in address reg.
"D=M\n" // D = prev. LCL value
"@LCL\n"
"M=D\n" // write prev LCL value to LCL
"// goto retAddr\n"
"@R13\n" // location of retAddr
"A=M\n" // A = retAddr
"0;JMP\n" // return
"\n";
// idea: make global function, "call" this function when doing 'return'
// similar to conditional branch (TODO)
fprintf(fp, "%s", ret_boilerplate);
return true;
}
static bool write_call(struct vm_instruction_t *vm_instr, FILE *fp)
{
uint16_t new_arg;
/*
* push retAddr // generates a label and pushes it to the stack
* push LCL // saves LCL of caller
* push ARG // saves ARG of caller
* push THIS // saves THIS of caller
* push THAT // saves THAT of caller
* ARG = SP - 5 - nArgs // repositions ARG
* LCL = SP // repositions LCL
* goto functionName // transfers control to the callee
* (retAddr) // injects the return address label into the code
*/
// Note: I use a different convention for generating return address
// labels. The book does FilenameFunctionname$ret.<0-n> for n returns,
// but the extra bookkeeping will annoy me. So I'll just use the current
// line number instead. This works because the function name also
// contains the file name, and the file name combined with a line number
// provides a uniqueness guarantee, so return addresses won't collide.
char call_boilerplate[] = "// push retAddr\n"
"@%s.%hu\n" // will format to retAddr
"D=A\n" // D = retAddr as constant
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n" // RAM[SP] = local pointer
"// push LCL\n"
"@LCL\n"
"D=M\n" // D = current local pointer
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n" // RAM[SP] = arg pointer
"// push ARG\n"
"@ARG\n"
"D=M\n" // D = current arg pointer
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n" // RAM[SP] = arg
"// push THIS\n"
"@THIS\n"
"D=M\n" // D = current this
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n" // RAM[SP] = this
"// push THAT\n"
"@THAT\n"
"D=M\n" // D = current that
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n" // RAM[SP] = that
"// ARG = SP - 5 - nArgs\n"
"@SP\n"
"D=M\n" // D = SP
"@%hu\n" // will format to (5 + nArgs)
"D=D-A\n" // D = SP - 5 - nArgs
"@ARG\n"
"M=D\n"
"// LCL = SP\n"
"@SP\n"
"D=M\n" // D = SP
"@LCL\n"
"M=D\n" // LCL = SP
"// goto functionName\n"
"@%s\n"
"0;JMP\n"
"// (retAddr)\n"
"(%s.%hu)\n"
"\n";
//print_vm_instruction(vm_instr, fp); // TODO remove me
new_arg = 5 + vm_instr->arg2; // probably breaks if arg2 > 32K lmfao
fprintf(fp, call_boilerplate, vm_instr->arg1, file_line_no,
new_arg, vm_instr->arg1,
vm_instr->arg1, file_line_no);
return true;
}
bool write_instruction(struct vm_instruction_t *vm_instr, FILE *fp)
{
fprintf(fp, "\n// %lu: %s\n", file_line_no, vm_instr->line);
switch (vm_instr->cmd) {
case C_ARITHMETIC:
return write_arithmetic(vm_instr, fp);
case C_PUSH:
return write_push(vm_instr, fp);
case C_POP:
return write_pop(vm_instr, fp);
case C_LABEL:
return write_label(vm_instr, fp);
case C_GOTO:
return write_goto(vm_instr, fp);
case C_IF:
return write_if(vm_instr, fp);
case C_FUNCTION:
return write_function(vm_instr, fp);
case C_RETURN:
return write_return(fp);
case C_CALL:
return write_call(vm_instr, fp);
default:
err("error: unrecognized instruction (%u)\n", vm_instr->cmd);
return false;
}
return false; // should never reach here tbh
}
#endif // _CODEWRITER_H
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